1. Field of the Invention
The present invention relates to a hydraulic pressure supplying device for a transmission, and more particularly to a hydraulic pressure supplying device for a transmission in a hybrid vehicle or the like having a main oil pump and an auxiliary oil pump such as an electric oil pump.
2. Description of the Related Art
There has recently been developed a vehicle having an engine adapted to be temporarily stopped for the purposes of improvement in fuel economy and emission reduction of carbon dioxide, such as a hybrid vehicle and a vehicle having an idling stop engine. In an automatic transmission (AT) mounted on such a vehicle, a mechanical oil pump for supplying oil to a hydraulic control unit in the automatic transmission is provided in interlocking relationship with the engine, so that the mechanical oil pump is stopped when the engine is stopped. In a hybrid vehicle, for example, an electric oil pump for supplying oil to the hydraulic control unit in an auxiliary manner is therefore provided to normally perform hydraulic control at starting of the vehicle.
Japanese Patent Laid-open No. Hei 11-287316 discloses a hydraulic pressure supplying device for a transmission including a first oil pump (main oil pump) adapted to be driven by a main shaft of the transmission, a second oil pump (auxiliary oil pump) adapted to be driven by an electric motor, and a check valve provided between the discharge side of the second oil pump and the discharge side of the first oil pump to prevent the flow of oil from the first oil pump to the second oil pump. In the hydraulic pressure supplying device disclosed in this publication, the first oil pump and the second oil pump are connected to individual strainers.
The hydraulic pressure supplying device disclosed in Japanese Patent Laid-open No. Hei 11-287316 mentioned above has the following problem. In the case that foreign matter is generated in the second oil pump because of chip scratching or the like or in the case that foreign matter is generated because of failure or the like of the hydraulic control unit in the transmission, there is a possibility that the foreign matter may cause adverse effects on the function of the check valve or the first or second oil pump.